Ikuo OHNUMA, Naohide KAMIYA, Yuji SUTO, Toshihiro OMORI,

Thermodynamic Database of High-Strength Low-Density Steels

Ryosuke KAINUMA and Kiyohito ISHIDA

Department of Materials Science,

Tohoku University, Sendai, JAPAN

TOFA2010, September 14, 2010 @Porto

Contents

� Thermodynamic Database of Steels.

� Application of Thermodynamic D.B. (1) Fe-Mn-Al-Cr-C System(2) Low-Density & High-Strength Steels

� Mechanical Properties of Low-Density & High-Strength Steels

Background: High-Strength & Low Density Steel

Thermodynamic Database of Steels for various Systems

Application of Thermodynamic D.B.- High-Strength Low-Density Steels

Alloy Design of Lightweight Steels

Effect of Alloying Elements on Density of γγγγ-Fe

Lightweight Steels by Al & SiEmbrittlement due to Ordering

Alloy Design of High-strength & Lightweight Steels

High-Strength Low-Density Steels：Thermodynamic D.B. ＋ Density

High-Strength Low-Density Steels：Density Calculation of γγγγ-Fe

Precipitation of κκκκ-carbide in γγγγ-Fe

Experimental Procedures

Homogenization（1200℃）℃ ℃

Alloys Induction Melting

Equilibrium Composition

EPMA(mass%C was determined by calibration curve method.)

Microstructure Optical Microscope

Heat TreatmentHomogenization（1200℃）Equilibration（800℃～～～～1200℃）

Thermodynamic Models

Liquid：Sub-regular Solution ApproximationSolids（γγγγ-Fe, αααα-Fe, κκκκ）：Sub-lattice Model

Large Solubility of κκκκ

Thermodynamic Modelsー L12 Ordering in FCC Phase

Liquid：Sub-regular Solution ApproximationSolids（γγγγ-Fe, αααα-Fe, κκκκ）：Sub-lattice Model

Thermodynamic Models

High-Strength Low-Density Steels：Thermodynamic D.B.

Results of Calculation (1)－－－－ Fe-Mn-Al System

R. Umino et al., J. Phase Equilibr.& Diffusion., 27 (2006) 54-62.

Results of Calculation (2)－－－－ Fe-Al-C System

Results of Calculation (3)－－－－ Mn-Al-C System

Results of Calculation (4)－－－－ Fe-Mn-Al-C System

High-Strength Low-Density Steels：Alloy Design

Strategy of Alloy DesignFe-Mn-Al-Cr-C Alloys.

(1) Reduce Density Light elements (Al, C & Mn)

γγγγ γ γ γ γ (2) Stabilize γγγγ-Fe γ γ γ γ stabilizing elements (C & Mn)

(3) Corrosion resist. Cr

(4) Precipitation of Appropriate aging & κκκκ-Carbide cooling

(1) Fe-Al-C ternary alloys: Alloy Design of Low-Density γγγγ-Fe

(2) Effect of Mn on Density & γγγγ-Fe－ Fe-8Al-1C +Mn

(2) Effect of Mn on Density & γγγγ-Fe－ Fe-10Al-1C +Mn

(3) Optimization of C content－ Fe-20Mn-xAl +C

(4) Optimization of Cr content－ Fe-20Mn-10Al-1.5C +Cr

(5) Summary of Alloy Design － Fe-20Mn-10Al-5Cr-1.5C Alloy

Experimental Procedures: Mechanical Properties

As-Quenched (W.Q.) Microstructure（Fe-20Mn-5Cr-10Al-1.5C）

Microstructures after A.C.（Fe-20Mn-5Cr-10Al-1.5C）

Results of Tensile Test（Fe-20Mn-5Cr-xAl-yC）

Microstructures by TEM（Fe-20Mn-5Cr-10Al-1.5C :1100℃℃℃℃）

<100> γ γ γ γ //<100> κκκκ

Low Work-Hardening (LWH)（Fe-20Mn-5Cr-xAl-yC）

Comparison of Mech. Properties with other materials

Summary

� Thermodynamic Database of Steels.⇒⇒⇒⇒ Fe-Mn-Al-Cr-C (-Si) System

� Application of Thermodynamic D.B. ⇒⇒⇒⇒

⇒⇒⇒⇒

� Application of Thermodynamic D.B. ⇒⇒⇒⇒ γγγγ-Fe + κκκκ-Carbide with

Low-Density（～6.6 g/cm3）� Mechanical Properties ⇒⇒⇒⇒ High-Strength（～1200MPa） &

Low Work Hardening Steels

Thank you for your attention. Thank you for your attention.

CALPHAD(CALculation of PHAse Diagrams)